textproduct: Quad Cities

KEY MESSAGES

- Hot and humid conditions are forecast to continue through Saturday with peak afternoon heat indices of mid-90s to low 100s. A Heat Advisory has been issued for counties along and south of Highway 34 between noon and 7PM Saturday where heat indices will likely (60-80%) exceed 100 degrees.

- Isolated to scattered showers and storms (20-50% coverage) are possible this afternoon/evening and Saturday morning/afternoon. Isolated severe storms are possible (5% chance) Saturday, mainly in west-central Illinois. - There will be Canadian wildfire smoke at times Saturday night into Sunday in the form of mainly hazy skies. However, thicker concentrations near-surface and unhealthy air quality is possible across parts of northwest Illinois through tonight.

- A cold front on Monday poses a severe weather threat, with the SPC issuing a Slight Risk (Level 2 out of 5) for potential damaging winds.

SHORT TERM /THROUGH SATURDAY NIGHT/

Issued at 143 PM CDT Fri Jul 17 2026

As the upper-level ridging over the area continues to break down, a weak shortwave will be pulled northward, boosting cloud cover and PoPs this afternoon into the overnight hours ahead of a cold front pushing southward into Minnesota and Wisconsin. Unlike previous days, the winds are forecast to be generally 5-10 mph across the area, but the southerly component will support weak warm air advection in the low levels. This keeps the heat around this afternoon with highs in the low-to-mid-90s besides the areas that see afternoon thunderstorms, and overnight lows are expected to be in the mid-70s ahead of the front.

An Air Quality Alert remains in effect until midnight tonight for Jo Daviess and Stephenson Counties. As winds shift out of the south this afternoon, any smoke or haze currently present over northwest Illinois will be advected northward, but smoke could return later into the weekend.

Heading into Saturday, the cold front is expected to clear the area from north to south before stalling near the Missouri-Iowa border overnight Saturday. Scattered thunderstorm development will be favored along this front, but the weak convergence and displacement of the low pressure system over southern Quebec should keep coverage isolated to scattered at 20-50%. In terms of severe weather, the SPC does have a Marginal Risk (Level 1 of 5) for west-central Illinois, far southeast Iowa, and northeastern Missouri where the front is forecast to be near during peak daytime heating. SBCAPE values in the range of 1500-2000 J/kg appear likely (60-90%), but the weak 0-6-km bulk shear around 20 knots should prevent significant organization of storms with the greatest hazard being gusty winds with any strong downbursts. The heat potential remains mainly along and south of Interstate 80 as drier air behind the cold front is forecast to dampen heat indices in our northern counties. A Heat Advisory has been issued for counties along and south of Highway 34 where heat indices will likely (60-80%) exceed 100 degrees for several hours prior to the cold front's arrival. If confidence increases on the northern side of the Heat Advisory, it could be expanded northward. By Saturday night, PoPs decrease with the loss of diurnal heating and dry air advection from the northerly winds as lows drop into the upper 60s to low 70s. However, the northerly winds could advect additional smoke from the Canadian and Minnesota wildfires into northwest Illinois and northeast Iowa and will need to be monitored.

LONG TERM /SUNDAY THROUGH FRIDAY/

Issued at 143 PM CDT Fri Jul 17 2026

Sunday...With a high pressure over the Great Lakes and a longwave trough over the eastern CONUS, subsidence returns to the area as the skies clear once again. Smoke/haze advection is expected to continue into northwestern Illinois and east-central Iowa. While smoke concentration amounts remain uncertainty, there is the potential for air quality to be impacted. Outside the smoke, temperatures and dew points are forecast to be lower thanks to Saturday's cold front, with highs in the 80s and dew points back into the mid-60s. These comfortable temperatures do not last long though as the next shortwave dives into south-central Canada Sunday night, deepening a new low pressure system over Manitoba and shifting our winds back out of the south.

Monday-Tuesday...The shortwave trough continues to propagate southeastward into Minnesota and Wisconsin as the low pressure shifts into Ontario, supported by the left-exit region of a 100 kt jet streak. An accompanying cold front is forecast to be pushed into the Minnesota and northern Iowa where convection will be favored in the warm air advection regime, especially along and north of Interstate 80 where there is the potential for storms to turn strong to severe. Looking at the latest LREF guidance, the joint probability of at least 1000 J/kg of SBCAPE and 35+ knots of sfc-to-500 mb bulk shear is 40-60%. There are signals of a potential MCS development along the retreating boundary from Saturday's cold front which is why the SPC has gone ahead and issued a Slight Risk (Level 2 of 5) for much of the CWA along and north of Highway 34. The area is subject to change with newer model runs, but the primary hazard with any organized convection will be damaging winds.

By Tuesday morning, the cold front should clear the area from northwest to southeast with thunderstorms mainly in Illinois during the morning hours, and by the afternoon, cold and dry air advection take over as winds shift to northwesterly and skies begin to clear. Highs will likely (80-100%) not even reach 90 along and north of Interstate 80 as lows Tuesday night sink into the upper 50s to mid- 60s (50-70% chance).

Wednesday-Friday...After Tuesday's cold front, the area gets a little bit of deju vu with a high pressure camping over the CWA, but unlike this past week, there will be no heat dome overhead. This means that the cooler, drier air mass will modify slowly through the end of next week with temperatures and dew points only creeping up a couple degrees each day. Even with mostly sunny skies, high temperatures and dew points will likely (70-100%) not exceed 90 degrees or 70 degrees, respectively, during this time period.

AVIATION /00Z TAFS THROUGH 00Z SATURDAY/

Issued at 603 PM CDT Fri Jul 17 2026

VFR conditions will prevail through much, if not all, of the TAF period. Light southwesterly winds tonight will increase after 12z Saturday ahead of an approaching cold front, with northwest winds behind the front. Along and ahead of the cold front, scattered showers/storms will be possible. Confidence on timing and coverage is low at this time. Thus, opted to cover with a PROB30 group at this time, with chances better at MLI and BRL.

DVN WATCHES/WARNINGS/ADVISORIES

IA...Heat Advisory from noon to 7 PM CDT Saturday for IAZ087>089- 098-099. IL...Heat Advisory from noon to 7 PM CDT Saturday for ILZ025-026- 034-035. Air Quality Alert until midnight CDT tonight for ILZ001-002. MO...Heat Advisory from noon to 7 PM CDT Saturday for MOZ009-010.